When installing carpet, it is common for the room in which the carpet is being installed to have at least one dimension (length or width) that is greater than the length of a standard roll of carpet (which is typically twelve feet). In such a case, a single unitary segment of carpet from a roll cannot cover the entire floor of the room, and two or more segments must be pieced together. When two or more segments are pieced together, an edge of one segment is abutted against an edge of another segment, and these edges are joined (“seamed”) together using seam tape.
FIGS. 1 and 2 illustrate top and cross-sectional views, respectively, of prior art seam tape. Prior art seam tape 10 comprises an elongated base layer 12, scrim 14, and an adhesive 16 (the adhesive is omitted from FIG. 1 for clarity). The base layer typically comprises paper or other relatively inelastic material. The scrim typically comprises woven threads and provides strength and additional inelasticity to the seam tape. The adhesive typically comprises a hot-melt thermoplastic adhesive applied to a large portion of the base layer. The scrim is embedded within the adhesive.
When joining carpet edges together, the edge of one carpet segment is positioned to abut the edge of the other carpet segment. The seam tape is positioned under the abutting edges, and the adhesive is activated by applying heat to the top surface of the carpet above the seam tape. The heat melts the adhesive and the melted adhesive bonds to the underside of both carpet segments as the adhesive cures.
After the carpet segments are positioned to cover the entire floor and the seams are joined using seam tape, the carpet is stretched at the outer edges and the outer edges are secured to the floor using tack strips. The stretching tightens the carpet to remove any slack and wrinkles. FIG. 3 illustrates what happens when the carpet is stretched in a direction transverse to the carpet seam (indicated by the arrows in FIG. 3). The top image of FIG. 3 illustrates the unstretched carpet. As the carpet is stretched and the two carpet segments 18A, 18B are pulled away from each other, the inelasticity of the seam tape 10 causes the seam to lift off the floor, resulting in an unsightly bulge in the carpet (illustrated in the bottom image of FIG. 3). This is called seam “peaking” or “profiling” and is highly undesirable.